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Today in the Garden of a Lifetime: Wisteria & Laburnum: The Classic Tango

Only the Asian forms of wisteria are in flower at the same time as the one form of laburnum you should grow before all others: Voss's. American wisterias typically flower two or three weeks later; today, when the laburnum is in its freshest flush, my "Americans" are just barely showing their buds whereas all my "Asians" are in full bloom. By the time American wisterias are in full flower, the all-too-short laburnum season will be past.

But to create a duo of wisteria and laburnum that really sings when in bloom, there are more choices of wisteria to be made than just Asian not American. Those laburnum flowers sing just one note, and it's chrome yellow. Wisteria flowers that are white don't have much in common with the saturated yellow of the laburnum. Wisteria flowers that are pink will be in strident conflict. Even wisteria flowers of the normal lavender shades could seem washed out.

Although it's still just a fantasy for any wisteria to have flowers that are as deeply hued as those of the laburnum—but in wisteria-appropriate colors of burgundy or purple or indigo—flowers of Wisteriasinensis 'Black Dragon' are a reasonable second choice.

Mature sepals and petals may be pale lavender, but when young they are grape-jelly purple.

Flowers of 'Black Dragon' have a profusion of extra petals; in the mature flower below, you can see that the only petal to retain the deep hue is the one at the bottom of the flower. It projects forward like an upward-facing scoop, and is known as the keel. The keel is often the darkest element of a wisteria flower; check again the pictures of long-chain wisteria: The keels are deep lavender, but the upper petals are a milky white that is only faintly lavender-tinged.

I also appreciate the contrast between the simple structure and solid coloring of the laburnum flowers, and the variable coloring and fluffy "petticoats" of the flowers of 'Black Dragon' wisteria.

Wisteria sinensis is, potentially, a gigantic woody vine, while Laburnum x watereri 'Vossii' is only a small ornamental tree at its biggest. But the wisteria should never be planted except when trained without mercy—and that training, happily, can easily limit the vine's extent enough to bring it into scale with the laburnum.

And although the laburnum can be grown free-standing, as a tree it's a stiff and (to my eye) crass and suburban thing. Plus, its flowers are its only glory. No, really: There's no Fall foliage color, nor interesting bark or seed pods, nor graceful branching. On its own, a laburnum is only interesting for two weeks of the year, which is a dismal record for narrow seasonal performance shared with another all-too-popular Spring bloomer: the lilac. But the laburnum's young stems are flexible, and are easy to fan out onto an espalier or pergola frame.

Training laburnum and wisteria to the same structure, then, limits the size of the wisteria while also providing an interesting shape to the laburnum. It ameliorates the downsides of each plant such that their spectacular flowers can be brought into close association—and right at center stage, too, when the garden's yearly cycle is just beginning, and such a full-on show is, automatically, the thrill of the fortnight.

My pergola has a single 'Black Dragon' at one end and a pair of 'Vossii' at the center, flanking the entry of a perpendicular path. I may add something else entirely to the pergola's other end—especially if that plant provides a show at any time other than mid-May. Or, wisteria being wisteria, I could train 'Black Dragon' the full length of the structure. For sure, I'll extend both the 'Black Dragon' and the pair of 'Vossii' such that their branches weave together.

Yes, this would mean even more attention to restraining the wisteria, lest its rambunctious growth bring blossom-reducing shade to the laburnum. I had considered suggesting that the laburnum stems be trained across the top of the crosspieces of pergola, and the wisteria stems across the bottom: Wisteria can bloom despite receiving part shade. But then the laburnum's racemes wouldn't reach down as far as those of the wisteria and, surely, one aspect of the thrill of these two plants' simultaneous flowering is that their racemes descend equally far.

How to weave the wisteria and laburnum together while also providing full sun to each? Don't, literally, weave them. Instead, train laburnum stems along every other pergola crosspiece, and train wisteria stems just along the interveners. Also, it's probably best to start the wisteria stems along the crosspieces from the other side of the pergola from where the laburnums are planted. Looking at the pergola from either side, you'd see a pendulous row of wisteria racemes, then one of laburnum, then the next of wisteria, then the next of laburnum. Looking down the length of the pergola, though, the effect is likely to be far more mingled and jostling. You'd be aware of the intimate juxtaposition of the two types of racemes, but with less sense that each plant's row of racemes was interdigitating with the other's.

My pergola is comparatively compact: Six feet wide and twenty feet long. If there were ever opportunity to pair these plants on a much larger structure, they could be planted in multiples and trained with even more striking geometry. What if wisteria stems were trained along the crosspieces while the laburnum stems were trained at ninety degrees to them, so that they crossed the crosspieces? (If the pergola canopy were a grid of squares, not just a row of parallel crosspieces, this training would be all the more easy to achieve.) From one side, with wisteria rows head-on and laburnum rows end-on, you'd see blocks of wisteria racemes with intervening rows of laburnum. Rotating your vantage ninety degrees, you'd see blocks of laburnum racemes and intervening rows of wisteria.

No matter how you array the wisteria and laburnum growth, part of the astonishment of this partnership of vine and tree is the careful training that the partnership requires. To achieve it, you've already needed to sign up for the tying and pinching and pruning. Those horses have been let out of the barn, then, right from the beginning. Why not use that same training—and the same amount of it—to create a flourish that is as much about geometry as color?

Here's how to grow Wisteria floribunda, which is the Japanese cousin of Wisteria sinensis. Its hardiness and handling are the same.